The present invention relates to an image processing system and a control method therefor, an image processing apparatus, and a recording medium and, more particularly, to an image processing system for forming a color image by an image forming apparatus on the basis of data transferred from an image processing apparatus and a control method for the system, an image processing apparatus, and a recording medium.
In recent years, networking of image processing apparatuses has progressed, and systems for data communication based on high-speed serial communication using IEEE 1394 (to be referred to as an IEEE 1394 scheme hereinafter) have emerged to realize high-speed transfer of a large quantity of image data.
High-speed serial communication such as IEEE 1394 or USB has an isochronous transfer mode capable of ensuring a given data transfer rate. More specifically, according to the isochronous transfer mode, a necessary number of channels for guaranteeing data transfer every defined cycle can be ensured. Hence, for example, in an image processing system having an image reading apparatus, computer, and image forming apparatus which are connected through an IEEE 1394 serial bus, image data can be transferred from the image reading apparatus to the computer or from the computer to the image forming apparatus by ensuring a predetermined transfer rate corresponding to the processing ability of each apparatus.
As an image forming apparatus constructing the above-described image processing system using a serial bus, an image forming apparatus for forming a color image by electrophotography is known.
A known color image forming apparatus using electrophotography repeats the image forming operation four times for yellow, magenta, cyan, and black using one photosensitive drum and a transfer drum, thereby forming a color image.
In the image processing system in which image data is transferred from a computer and an image is formed on printing paper using such one-drum image forming apparatus, after the printing paper is wound on the transfer drum, image data for yellow image formation is transferred first to form an image. Next, image data for magenta image formation is transferred to form an image, image data for cyan image formation is transferred to form an image, and finally, image data for black image formation is transferred to form an image. After that, the printing paper is removed from the transfer drum, and the images are fixed to print the color image.
In the image processing system using the one-drum color image forming apparatus, one set of mechanisms such as a photosensitive drum necessary for image formation suffices. Since color image data can be transferred four times, the apparatus need not be equipped with a large-capacity image memory required to temporarily store the color image data although high-speed printing is difficult. For this reason, color printing can be realized with a relatively inexpensive arrangement.
Another known color image forming apparatus using electrophotography uses four photosensitive drums for yellow, magenta, cyan, and black and forms an image once per drum to form a color image.
In an image processing system in which image data is transferred from a computer and an image is formed on printing paper using such four-drum image forming apparatus, after image data of yellow, magenta, cyan, and black sent from the computer are temporarily stored in image memories for the respective color image data, the color image data are sequentially read out from the image memories to form images in accordance with timings for conveying printing paper to the respective photosensitive drums. After this, the images are fixed to print the color image.
In the image processing system using the four-drum image forming apparatus, a color image can be formed by conveying printing paper once. For this reason, printing at a relatively high speed can be realized.
For example, given a system which connects one computer to a plurality of image forming apparatuses as the image processing system using a serial bus, image data can be transferred from the computer to the plurality of image forming apparatuses by ensuring a necessary number of channels of a transfer mode such as the isochronous transfer mode capable of ensuring a data transfer rate, and an image can be formed.
In this case, however, the computer outputs image data without control, i.e., transfers data to ensured channels without handshaking. Each of the plurality of image forming apparatuses connected must have a large-capacity memory to establish synchronization with data transfer from the computer so as to compensate for a synchronization shift between the image forming apparatuses. The image forming apparatuses and system become expensive because of the image memories.
For image data transfer from the computer to the plurality of image forming apparatuses in the system, if channels of the isochronous transfer mode are individually ensured for the image forming apparatuses for data transfer, synchronization adjustment using the large-capacity image memories of the image forming apparatuses is unnecessary. In this case, however, the number of channels to be ensured increases in accordance with the number of image forming apparatuses, resulting in occupation of channels in the isochronous transfer mode.
In the four-drum image forming apparatus, the photosensitive drums are spaced apart from each other by a predetermined distance for reasons of mechanical arrangement, and printing paper is conveyed sequentially through the plurality of photosensitive drums. Hence, image data of the respective colors must be supplied while correcting any time lags between the times of arrival of the printing paper at the photosensitive drums. In addition, differences in the image formation position between the photosensitive drums, i.e., so-called misregistration must be corrected. To do this, synchronization adjustment between the color image data and fine adjustment of the image formation positions must be performed using a large-capacity image memory or FIFO memory for temporarily storing image data. Hence, the cost of the image forming apparatus inevitably increases.
In the image processing system including a four-drum image forming apparatus as well, when the channels in the isochronous transfer mode are individually ensured for the plurality of photosensitive drums in the image forming apparatus, as described above, synchronization adjustment between the photosensitive drums using a large-capacity image memory need not be performed. However, four channels must be ensured for each photosensitive drum of each image forming apparatus. Hence, the number of channels required further increases, resulting in occupation of channels of the isochronous transfer mode.
Accordingly, it is an object of the present invention to provide an image processing system in which an image processing apparatus and image forming apparatus are connected via a serial bus, and the image forming apparatus with an inexpensive arrangement can print, at a high speed, image data transferred from the image processing apparatus in the isochronous transfer mode, a control method for the image processing system, an image processing apparatus, and a recording medium.
According to the present invention, the foregoing object is attained by providing an image processing apparatus connected to a plurality of image forming apparatuses via a serial bus, comprising:
channel control means for ensuring a plurality of channels for isochronous transfer through said serial bus and assigning the channels to a plurality of types of image data on the basis of device information of said plurality of image forming apparatuses; and
communication means for isochronously transferring the plurality of types of image data to said plurality of image forming apparatuses using the assigned channels.
The foregoing object is also attained by providing an image processing system in which an image processing apparatus and a plurality of image forming apparatuses are connected via a serial bus,
the image processing apparatus comprises:
channel control means for ensuring a plurality of channels for isochronous transfer through said serial bus and assigning the channels to a plurality of types of image data on the basis of device information of said plurality of image forming apparatuses; and
first communication means for isochronously transferring the plurality of types of image data to said plurality of image forming apparatuses using the assigned channels, and
each of said plurality of image forming apparatuses comprises:
second communication means for receiving the plurality of types of image data isochronously transferred using the channels via said serial bus; and
image formation means for forming an image on a recording medium on the basis of the received plurality of types of image data.